Generally, a vacuum transfer system means a system that actuates a vacuum pump with compressed air, discharges internal air from a suction cup coming into contact with a surface of an article, holds the article using negative pressure that is thus obtained, and transfers the article to a predetermined position. In this regard, the suction cup is coupled to an end of a pipe member that is separately provided, and is connected to the vacuum pump via this member. The suction cup includes a ring-shaped connector and a skirt-shaped pad coupled to a lower portion of the connector.
The pad is usually formed of a soft material such as rubber or urethane. Traditionally, the pad is integrally joined or secured to the connector using an adhesive or in an insert molding method. Such a kind of suction cup is useful even now.
However, this suction cup is problematic in that a gap may be formed in a junction between the connector and the pad when it is used for some time, so that external air may be introduced into the gap.
Further, this suction cup is problematic in that, even though only the pad is damaged, the entire suction cup should be replaced.
Conventionally, a so-called pressure ring was used to solve the above-described problems. That is, in the state where an upper end of the pad is coupled to an outer surface or an inner surface of the metal connector, the pressure ring is forcibly fitted over a surface of the flexible pad to strongly push the pad and thereby allow the connector to be in close contact with the pad. Vacuum cups disclosed in Korean Patent Nos. 932775, 1068954, 1195176 and the like belong to these examples. Indeed, the suction cup configured as such is useful to prevent vacuum leakage.
However, this is problematic in that the pad may be damaged during the assembly of the pressure ring, and it is virtually impossible or difficult to separate the pressure ring and the pad after they are assembled.
Meanwhile, a pad-separable suction cup has been proposed. Its example is found in a suction cup that is disclosed in US Patent Application Publication No. US 2012/0025053. This will be described in brief with reference to FIG. 1. This disclosed suction cup 1 includes a connector 2 and a pad 4 that are separably assembled with each other via an annular groove 3 and a projection 5 corresponding thereto, and a bellows 6 that is optionally assembled between the connector 2 and the pad 4.
In comparison with the conventional suction cup, the disclosed suction cup naturally ensures that the ‘separation’ of the flexible pad is relatively convenient.
However, this is problematic in that it is considerably inconvenient to ‘assemble’ the pad 4, and a coupling between the components 2 and 4 is weak, so that the vacuum leakage may occur in the assembled portion.
When the article is actually held and transferred, the pad 2 may be bent at upper and lower positions. In this case, a gap or an interstice may occur in the assembled portion of the pad 2, thus leading to vacuum leakage from the assembled portion. Moreover, since the connector 2 and the pad 4 are a flexible material, the pad 4 may be unexpectedly separated by a side load of the article.